Our goal is to study the alveolus from the perspective of four scientific disciplines (chemistry, cell biology, morphology and physiology) and thus to define its development and maturation, its adaptation to air breathing, its normal condition in situ, and its condition in selected abnormal states Specifically, the plan is to (1) determine the chemical composition ("the surfactant system") of the alveolar lining layer, the molecular basis for its role in normal pulmonary function, the natural history of its formation at birth, the pathological consequences of its disruption, and the possible use of isolated components for diagnostic and therapeutic purposes; (2) determine the molecular and subcellular basis of alveolar epithelial function; its role in the synthesis of components of the surfactant system, its adaptations to toxic environments, and its response to natural and iatrogenic stimuli; and (3) define the natural relationship between alveolar function at the cellular level and pulmonary integrity at the organ level; the way in which disturbances of this relationship result in disease and possible modes of prevention and therapy. The subjects of this research range from animals to human and from the developing fetus to the adult. The range of material is from subcellular particles to the intact organism. The focus is the alveolus, normal and abnormal.